Harmonization and comparison of soil chemical properties of the LUCAS topsoil database and the Hungarian National Soil Monitoring System

The European Joint Programme Cofound on Agricultural Soil Management has set the goal of harmonizing national soil databases with the continental LUCAS topsoil database for the purpose of monitoring soil carbon, fertility and land degradation. Up-to-date soil surveys have poor spatial resolution and are very cost- and labour intensive, so harmonizing the existing datasets allows us to create more accurate soil maps with better resolution. The LUCAS topsoil database can be used to complement the Hungarian Soil Information and Monitoring System (SIMS) for the creation of more detailed soil-property maps. Due to the different laboratory analysis methods and sampling strategies used by the two databases, conversion was needed, so the datasets can be directly compared to each other and used together for digital soil mapping. Two sets of topsoil data were used from 2009 and 2015 from both LUCAS and SIMS respectively, so the swiftly changing soil properties (pH, CaCO3, OC, P, K) were available for a more accurate side-by-side comparison. Map products were created for the chemical soil properties of both the LUCAS and SIMS database with the ancillary data of 28 environmental covariates using random forest kriging with 10-fold cross-validation. The spatial resolution of the maps was 100 x 100 m. The raster maps were compared directly to each other using linear regression. In conclusion the results show that the LUCAS and national soil databases can and should be harmonized, merged and used together for creating more accurate soil maps with better spatial resolution at national and continental scale.